1. Field of the Invention
The present invention relates to a variable displacement compressor used for compressing refrigerant in a refrigeration cycle of an automobile air conditioner or the like, comprising an airtight crank chamber and a variable inclination angle swing body installed on an axis of rotation inside said crank chamber, comprising at least one piston reciprocally guided in a cylinder and connected to said swing body, said cylinder being selectively connectable to a suction chamber in turn connected to a low-pressure refrigerant pipe conduit or to a discharge chamber in turn connected to a low-pressure refrigerant pipe conduit, and means in said variable displacement compressor for varying the amount of discharge of said refrigerant into said discharge chamber between a minimum discharge amount in a minimum operation state of the compressor and a maximum discharge amount by varying the angle of inclination of said swing body corresponding to a change of a pressure within said crank chamber, and further comprising a main valve between said low-pressure refrigerant pipe conduit and said suction chamber, said main valve being actuable between a fully closed state and a fully opened state.
2. Description of the Related Art
As the compressor used in a refrigeration cycle of an automobile air conditioner has a belt directly connected to the engine by a transmission belt, the number of its rotations cannot be controlled independently from engine speed. So a variable displacement compressor is used which can change the amount of refrigerant (the amount of discharge) to obtain the appropriate cooling capacity without being restricted by the number of rotations of the engine. In such a variable displacement compressor, a swing plate is generally installed in an airtight crank chamber so as to be able to tilt over a variable angle of inclination. The swing plate is driven by rotational movement of the axis of rotation and executes swing movements. A piston executing reciprocal motions by the swing movements of the swing plate sucks refrigerant of a suction chamber connected to a low-pressure refrigerant pipe conduit into a cylinder, compresses it, and discharges it to a discharge chamber connected to a high-pressure refrigerant pipe conduit. The amount of discharge of the refrigerant is changed by changing the angle of inclination of the swing plate according to change of pressure of the crank chamber. The variable displacement compressor used for a refrigeration cycle of an automobile air conditioner generally continues to operate even when cooling capacity is not needed, with a minimum displacement which is about 5% of the maximum displacement. That is, the compressor then operates at the minimum operation state. However, if simply operated like that, the problem occurs that even at the minimum operation state fins of the evaporator freeze when the load is small as in winter, due to a flow of compressed refrigerant into the evaporator. So, a valve is installed to enable a passage between the low-pressure refrigerant pipe conduit and the suction chamber to be fully closed, thereby preventing the low-pressure refrigerant from being sucked into the compressor at the minimum operation state. The conventional variable displacement compressor used in a refrigeration cycle of an automobile air conditioner makes the passage between the low-pressure refrigerant pipe conduit and the suction chamber to be fully closed at the minimum operation, irrespective of the season. However, freezing of the fins of the evaporator is a problem which occurs only when the load is small, as in winter. The problem of freezing does not occur, when the load is higher, as in summer. The load of the compressor for the engine produced by having closed the inlet of the compressor leads to a disadvantageous result because fuel efficiency decreases.